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RHEOLOGY REVIEWS 2003

ISBN: Book: 0-9538904-8-1 CD: 0-9547414-0-4

  • Rheology Reviews 2003
    pp. 1-36
    A REVIEW OF THE RHEOLOGY OF FILLED VISCOELASTIC SYSTEMS
    Howard A. Barnes

    PDF (click to download) Abstract (click to view)

    We are concerned here with the effect of added filler particles on the linear and non-linear rheological properties of viscoelastic systems. Whilst the addition of spherical or near-spherical filler particles will almost always increase the level of both the linear and the non-linear viscometric properties (so leading to increases in pressure drops, etc.), we usually find a decrease in the level of the elasticity (in its various measures combining the first normal stress difference and the shear stress), as manifested in such important practical features such as extrudate swell, melt fracture, size of entry vortices, stress relaxation, Weissenberg effect, etc. However, the addition of high-aspect-ratio, fibre-like fillers can increase the elasticity as well as the viscosity. Occasionally, the absorption of chemical species from the continuous phase onto the surface of the disperse phase particles can complicate matters due to depletion of the continuous phase.

  • Rheology Reviews 2003
    pp. 37-75
    SIMPLE NON-EQUILIBRIUM THERMODYNAMICS: APPLICATIONS TO POLYMER RHEOLOGY
    Anthony N. Beris

    PDF (click to download) Abstract (click to view)

    We review here recent developments in non-equilibrium thermodynamics and their applications to rheology.
    In particular we review the application of the dissipative Hamiltonian formalism to incompressible, homogeneous and isothermal flows of flexible polymer systems. We show not only the advantages that have been brought up by the non-equilibrium thermodynamics approach but also exactly where the actual contributions are in combination from a variety of specific modeling examples ranging from simple, one-conformation models to most recent coupled multivariable examples. In all cases, special attention is paid to convey the physical significance of the models through a close association to a more detailed microscopic interpretation.

  • Rheology Reviews 2003
    pp. 77-123
    RHEOLOGY OF MOBILE INTERFACES
    Gerald G. Fuller

    PDF (click to download) Abstract (click to view)

    This review discusses the rheology of interfaces that separate two, immiscible fluids. Unlike interfaces at the fluid/solid boundary, these surfaces are mobile and deform. In the presence of amphiphiles that collect at these interfaces, they can become highly structured and non-Newtonian. These nonlinear responses to flow have profound implications on many physical processes and examples can be found in nature and industry. This review summarizes experimental methods in interfacial rheometry (both mechanical and optical methods are discussed), and presents their application to numerous classes of complex fluid interfaces. These interfaces come in a wide range of forms that are often directly analogous to their three-dimensional counterparts. This review presents results on classical fatty acids and alcohols, multiphase systems, rodlike amphiphiles, flexible chain amphiphiles, surface gelation, biopolymers, and two-dimensional suspensions.

  • Rheology Reviews 2003
    pp. 125-165
    COMPRESSIVE RHEOLOGY: AN OVERVIEW
    Ross G. de Kretser, David V. Boger & Peter J. Scales

    PDF (click to download) Abstract (click to view)

    Compressive rheology, or the behaviour of suspensions in sedimentation and compression has been widely studied and many theories, using different physical quantities, have evolved in parallel. This review article provides a basis for the reconciliation of these approaches via presentation of the Buscall-White (1987) approach to consolidation, which uses a compressive yield stress, Py(φ), and a hindered settling factor, R(φ), to quantify the strength of a particle network in compression and the inter-phase drag respectively, and linking it to other theories and related de-watering parameters available in the literature. The links between behaviour of a concentrated particle system in shear and compression are then discussed and a review of the various experimental methods available for determination of the de-watering parameters is presented. The final section overviews the practical application, benefits and limitations of models for real de-watering processes.

  • Rheology Reviews 2003
    pp. 167-195
    FINITE ELEMENT METHODS FOR INTEGRAL VISCOELASTIC FLUIDS
    Roland Keunings

    PDF (click to download) Abstract (click to view)

    We review the field of finite element techniques for solving complex flows of viscoelastic fluids described by a constitutive model of the integral type. The focus is mainly put on mathematical formulations and numerical approaches. A short guide to published simulations of non-trivial flow problems is offered.

  • Rheology Reviews 2003
    pp. 197-233
    PRESENT PUZZLES OF ENTANGLED POLYMERS
    Tom C. B. McLeish

    PDF (click to download) Abstract (click to view)

    Entangled polymeric fluids, including high molecular weight polymer melts, constitute a fundamental example of viscoelastic fluids. In spite of enormous advances in understanding the molecular origin of their rheology and microscopic dynamics, there are several pressing puzzles, some of them strongly linked, that offer current and pressing challenges. We review the current state of the field and nature of five current challenges.

RHEOLOGY REVIEWS 2004

ISBN: Book: 0-9538904-9-X CD: 0-9547414-1-2

  • Rheology Reviews 2004
    pp. 1-17
    FAILURE AND RECOVERY OF ENTANGLED POLYMER MELTS IN ELONGATIONAL FLOW
    Yogesh M. Joshi & Morton M. Denn

    PDF (click to download) Abstract (click to view)

    Entangled polymer melts exhibit failure in elongational flow, with different failure modes characteristic of different Weissenberg number regimes. Theoretical attempts to predict failure include Reiner's dynamical theory of strength, the Considère construction for the onset of necking, and a scaling theory that associates rupture with a critical recoverable strain. Reiner's theory is not consistent with the overall trend of available data, and the Considère construction does not appear to be applicable to melt flow in regimes with dissipation. The scaling theory is in qualitative agreement with available data but falls short quantitatively, and predictive capability of failure in elongational flow remains an elusive goal. An understanding of rupture and its relation to recovery, if any, is hindered by the extremely limited experimental database on rupture and recovery of well-characterized polymers.

  • Rheology Reviews 2004
    pp. 19-65
    RHEOLOGY OF FOOD DISPERSIONS
    Críspulo Gallegos, José M. Franco & Pedro Partal

    PDF (click to download) Abstract (click to view)

    We review the viscous and viscoelastic behaviours of concentrated food emulsions and plant food suspensions. Special attention has been given to the influence that food processing exerts on the rheological characteristics of the above-mentioned foodstuffs.

  • Rheology Reviews 2004
    pp. 67-98
    MICRO-MACRO METHODS FOR THE MULTI-SCALE SIMULATION OF VISCOELASTIC FLOW USING MOLECULAR MODELS OF KINETIC THEORY
    Roland Keunings

    PDF (click to download) Abstract (click to view)

    We survey the field of micro-macro numerical techniques for predicting complex flows of viscoelastic fluids. The micro-macro approach couples the mesoscopic scale of kinetic theory to the macroscopic scale of continuum mechanics. A numerical solution is sought to the coupled non-linear problem involving the conservation laws and a microstructural model of kinetic theory. Although micro-macro techniques are much more demanding in terms of computer resources than conventional continuum computations, they allow the direct use of kinetic theory models in flow simulations, thus avoiding potentially inaccurate closure approximations. The focus of our survey is mainly put on mathematical formulations and numerical approaches. Applications to polymer solutions and melts, liquid crystalline polymers, and fibre suspensions, are briefly reviewed.

  • Rheology Reviews 2004
    pp. 99-142
    DYNAMICS OF A LIQUID DROP IN A FLOWING IMMISCIBLE LIQUID
    Stefano Guido & Francesco Greco

    PDF (click to download) Abstract (click to view)

    In this article we discuss the dynamics of a single drop immersed in an immiscible fluid with a given velocity field at infinity. Drop relaxation is also discussed. Newtonian and non-Newtonian fluid components are considered, to examine the effects of constitutive elasticity on drop deformation modes. Both experimental and theoretical results are reviewed. We illustrate in some detail three main issues of research of the last decade, namely, the exploitation of rheo-optical techniques, the study of large deformations and break-up, through numerical simulations, and the advancements in single drop theory for the case of non-Newtonian fluid components.

  • Rheology Reviews 2004
    pp. 143-170
    DRAG REDUCTION IN TURBULENT FLOW OF POLYMER SOLUTIONS
    Michael D. Graham

    PDF (click to download) Abstract (click to view)

    Progress in understanding turbulent drag reduction by polymer additives has recently been made on several fronts. The near-wall dynamics of Newtonian turbulence is becoming better understood. Detailed computations of complex flows of model polymer solutions are now possible. Insights into the effects of viscoelasticity have been gained from a number of important model flows, and the understanding of the dynamics of dilute polymer solutions, as well as the ability to perform detailed simulations of them, is maturing. We review the advances in these fronts and illustrate their contributions to the understanding of both turbulence and drag reduction. Finally, we highlight open questions and propose a general conceptual framework that would, if validated, unify observations of drag reduction from turbulence onset to the maximum drag reduction asymptote.

  • Rheology Reviews 2004
    pp. 171-196
    SELF-SIMILAR BREAKUP OF NON-NEWTONIAN LIQUID JETS
    Michael Renardy

    PDF (click to download) Abstract (click to view)

    We review similarity solutions to describe the asymptotics of the approach to breakup in non-Newtonian liquid jets. Both creeping flow and flow with inertia are considered for a variety of constitutive models. New phenomena in some models of non-Newtonian flows include the possibility of a jet breaking up simultaneously over a finite length, as well as a purely elastic breakup mechanism in which surface tension plays no role.

  • Rheology Reviews 2004
    pp. 197-223
    RECENT DEVELOPMENTS ON THE SLOW VISCOELASTIC FLOW PAST SPHERES AND BUBBLES
    B. Caswell, O. Manero & B. Mena

    PDF (click to download) Abstract (click to view)

    A review is presented covering the latest contributions to the slow viscoelastic flow past solid spheres and bubbles. The existing theoretical approaches are reviewed together with the available numerical methods. The proximity of container walls and its effect upon the motion of a sphere is also considered. Emphasis has been made on presenting recent experimental and numerical work intended to address some of the unresolved issues in this classic topic. Besides the so called "benchmark" problem of a viscoelastic fluid past a solid sphere centered on the axis of a long cylinder, this review addresses outstanding problems such as the wake behind the sphere, the negative wake, the depleted region effect as well as presenting some new results regarding the jump discontinuity in the velocity of rising bubbles.

RHEOLOGY REVIEWS 2005

ISBN: Book: 0-9547414-2-0 CD: 0-9547414-3-9

  • Rheology Reviews 2005
    pp. 1-48
    VISCO-ELASTO-CAPILLARY THINNING AND BREAK-UP OF COMPLEX FLUIDS
    Gareth H. McKinley

    PDF (click to download) Abstract (click to view)

    The progressive break-up of an initially stable fluid column or thread into a number of smaller droplets is an important dynamical process that impacts many commercial operations from spraying and atomization of fertilizers and pesticides, to paint application, roll-coating of adhesives and food processing operations such as container- and bottle-filling. The progressive thinning of a fluid filament is driven by capillarity and resisted by inertia, viscosity and additional stresses resulting from the extensional deformation of the fluid microstructure within the thread. In many processes of interest the fluid undergoing break-up is non-Newtonian and may contain dissolved polymer, suspended particles, surfactants or other microstructural constituents. In such cases the transient extensional viscosity of the fluid plays an important role in controlling the dynamics of break-up. The intimate connection between the degree of strain-hardening that develops during free extensional flow and the dynamical evolution in the profile of a thin fluid thread is also manifested in heuristic concepts such as "spinnability", "tackiness" and "stringiness". In this review we survey recent experimental and theoretical developments in the field of capillary-driven thinning and break-up with a special focus on how quantitative measurements of the thinning and rupture processes can be used to quantify the material properties of the fluid. As a result of the absence of external forcing, the dynamics of the necking process are often self-similar and observations of this "self-thinning" can be used to extract qualitative, and even quantitative, measures of the transient extensional viscosity of a complex fluid.

  • Rheology Reviews 2005
    pp. 49-100
    RHEOLOGY OF SOLID POLYMERS
    Igor Emri

    PDF (click to download) Abstract (click to view)

    The mechanical properties of solid polymeric materials quite generally depend on time, i.e., on whether they are deformed rapidly or slowly. The time dependence is often remarkably large. The complete description of the mechanical properties of a polymeric material commonly requires that they be traced through 10, 15, or even 20 decades of time. The class of polymeric materials referred to as thermo-rheologically and/or piezo-rheologically simple materials allows use of the superposition of the effects of time and temperature and/or time and pressure in such materials as a convenient means for extending the experimental time scale. This paper presents a critical review of models proposed to describe the effect of temperature and/or pressure on time-dependent thermo-rheologically and/or piezo-rheologically simple polymeric materials. The emphasis here is on the theoretical aspects, although experimental results are used as illustrations wherever appropriate.

  • Rheology Reviews 2005
    pp. 101-145
    RHEOLOGY AND MORPHOLOGY DEVELOPMENT IN IMMISCIBLE POLYMER BLENDS
    Peter Van Puyvelde & Paula Moldenaers

    PDF (click to download) Abstract (click to view)

    In this review, progress towards a fundamental understanding of the rheology-morphology relationship in immiscible polymer blends is discussed. The behaviour of biphasic polymer fluids, containing Newtonian components and subjected to simple shear flows is relatively well understood at present. The behaviour of these "simple" blends will be discussed first, as it serves as a reference for the other sections. In this overview, we will focus on studies that try to incorporate more complex but also more realistic aspects of blend behaviour. Firstly, structure development in compatibilized blends will be reviewed. Secondly, morphology generation in blends with viscoelastic components will be discussed. Thirdly, since blends are typically processed in mixing equipment in which the flow field is a complex combination of shear and elongation, the microstructural evolution in complex flow fields certainly deserves some attention. This includes the behaviour of polymer blends during special diagnostic flow conditions i.e. upon flow reversal and during LAOS. The overview closes with a discussion of blend morphology development in confined geometries.

  • Rheology Reviews 2005
    pp. 147-172
    BUBBLE DYNAMICS AND CAVITATION IN NON-NEWTONIAN LIQUIDS
    Emil A. Brujan & P. Rhodri Williams

    PDF (click to download) Abstract (click to view)

    Cavitation phenomena play important roles in many areas of science and engineering. The most interesting effect of the non-Newtonian properties of the liquid is the reduction of cavitation damage and noise. This article reviews experimental and theoretical efforts to understand such phenomena. The currently available information favors a description of the observed reduction of cavitation damage caused by a reduction of the pressure inside the bubble at its minimum volume, leading to a weaker shock wave emission during bubble rebound. After a brief historical review, the authors survey the major areas of research: Section 2 describes the dynamics of cavitation bubbles oscillating in a liquid of infinite extent, while Section 3 describes research on the behaviour of bubbles collapsing near rigid walls. Section IV discusses the role of the non-Newtonian properties in determining the cavitation threshold. The review also outlines some directions for future research.

  • Rheology Reviews 2005
    pp. 173-240
    APPLIED RHEOLOGY IN THE PROTECTIVE AND DECORATIVE COATINGS INDUSTRY
    Richard R. Eley

    PDF (click to download) Abstract (click to view)

    The success of a wide range of commercial products and industrial processes depends on meeting specific flow requirements. Industrial applied rheology attempts to relate fundamental properties to fitness-for-use of fluids of commerce. Architectural and industrial coatings, molded plastics, adhesives, personal care products and cosmetics, inks, cement, drilling muds, ceramic slips, solder pastes, foodstuffs and medicines are examples of rheologically complex fluids whose commercial viability depends on having the "right" rheology. For such materials, the necessary rheological properties must be defined with due regard to the prevailing conditions of stress and strain rate in processing and application. Unfortunately, the predominant practice in industry with respect to rheological characterization is to rely on rugged but simple viscometers or "viscometry devices". These typically measure within a limited range of stress or strain rate, generally returning arbitrary numbers of uncertain value. On the other hand, it is often very difficult to link fundamental rheological properties with "real-world" performance. The challenge to the applied rheologist is to design experiments having relevance to the process at hand and then usefully apply the result - in other words, to bridge rheology and technology. This article discusses the use of, in particular, controlled-stress rheometry to characterize complex fluids, with the main thrust toward the coatings industry.

RHEOLOGY REVIEWS 2006

ISBN: Book: 0-9547414-4-7 CD: 0-9547414-5-5

  • Rheology Reviews 2006
    pp. 1-60
    THE RHEOLOGY OF HIGH ASPECT RATIO NANO-PARTICLE FILLED LIQUIDS
    David W. Litchfield & Donald G. Baird

    PDF (click to download) Abstract (click to view)

    The objective of this review is to elucidate the recent developments in the rheology of suspensions containing high aspect ratio ( > 100 ) nano-scale fillers. In particular, this review focuses on industrially important nanoparticles, namely layered silicates or nanoclays, carbon nanotubes, and carbon nanofibers, suspended in low and high molecular weight liquids. This review begins with the critical aspects of nanoparticle structure. In addition, the surface chemistry is discussed in the context of particle-particle interactions leading to flocculation or aggregation, because optimum suspension properties occur in well-dispersed, non-aggregated systems. A comprehensive review of large aspect ratio nanoparticles in low and high molecular weight liquids is then presented, with discussions of the effects of particle size, surface treatment, meso-structural development on linear and non-linear viscoelastic properties (complex, steady shear, and extensional viscosity; shear thinning; stress overshoot; and primary normal stress difference where applicable). These sections elaborate on the following results of nanoparticle suspensions. First, nanocomposites require much lower concentrations for the same rheological effects as conventional micro-composites, because of the nanoparticle's larger available surface area and the development of a meso-structural polymer-nanoparticle network. Second, the linear viscoelastic properties generally increase with the addition of nanofiller, and the nanoparticles profoundly broaden the relaxation dynamics of the polymer melt. Third, the primary normal stress difference (N1) becomes negative at high stresses and high nanoparticle loadings. Finally, nanoparticles increase the values of extensional viscosity as a function of Hencky strain to a greater extent than micron sized fillers. This review concludes with a discussion of recent theory concerning particle network development and the nature of particle-polymer interactions with an emphasis on what types of constitutive relations are needed to describe the rheology of fluids containing high aspect ratio nanoparticles.

  • Rheology Reviews 2006
    pp. 61-130
    RHEOLOGY OF FRESH CEMENT AND CONCRETE
    P.F.G. Banfill

    PDF (click to download) Abstract (click to view)

    Cement-based materials are of enormous technological importance and their satisfactory performance depends on being able to transport and mould them in the freshly mixed state. This article describes the rheology of fresh cement, mortar, concrete and related products in the context of practical situations, and deals with testing and measurement, together with the main features of their behaviour. It explores the links between rheology and technology, and identifies areas where these are weak and could benefit from further experimental and computational effort.

  • Rheology Reviews 2006
    pp. 131-164
    INSTABILITIES IN EXTENSIONAL DEFORMATION POLYMER PROCESSING
    Hyun Wook Jung & Jae Chun Hyun

    PDF (click to download) Abstract (click to view)

    Instabilities in extensional deformation polymer processing have been reviewed focusing on the draw resonance, a Hopf bifurcation instability frequently occurring in hyperbolic systems. This draw resonance instability is usually one of the most industrially important productivity issues as well as the academically intriguing stability problem because its nonlinear dynamics is complicated and it always affects in a profound way the typical continuous polymer processing such as fiber spinning, film casting and film blowing where extensional deformation plays a dominant role in shaping and imparting desirable properties to the final polymer product. Experimental and theoretical results on draw resonance instability reported in the literature during the past four decades have been reviewed starting from the first discovery and naming as such in experimental observations, and the first theoretical modeling of each process, and then ending with pertinent recent research results. Also, the most important research topics and directions to be pursued in the future for each process are explained with highlights on several recent results that are showing crucial, relevant progress.

  • Rheology Reviews 2006
    pp. 165-216
    MOLECULAR DYNAMICS SIMULATION AND ITS APPLICATION TO NANO-RHEOLOGY
    Ahmad Jabbarzadeh & Roger I. Tanner

    PDF (click to download) Abstract (click to view)

    Over the last 15 years molecular dynamics (MD) simulations have become one of the important tools to tackle many of the complex problems that are faced by rheologists and engineers. The advent of modern areas of science such as nano-technology and the need to understand physical phenomena including rheology and tribology at the molecular scale have helped the growth of research both experimentally and computationally at nano-scales. Molecular dynamics simulations among other molecular simulation methods have been used for computational research in those areas. Application of molecular dynamics to rheology has helped to understand the behaviour of polymers qualitatively; also important progress has been made in predicting quantitative rheological properties such as the viscosity of simpler liquids (such as alkanes). In particular the application of MD to the behaviour of confined fluids and lubricants at nano-scales has revealed some important properties and explained the underlying physics of observed phenomena that include enhanced viscosity and relaxation times and the role of normal stress differences in supporting large loads. MD has been a valuable tool in studying the relationship of the molecular structure and the rheological properties. In this review we will give an introduction about the method and will discuss some of the progress made to date. Our main focus will be on the application of MD in the nano-rheology of ultra-thin confined films.

  • Rheology Reviews 2006
    pp. 217-253
    THE RHEOLOGY OF WORM-LIKE MICELLAR FLUIDS
    V. J. Anderson, J. R. A. Pearson & E. S. Boek

    PDF (click to download) Abstract (click to view)

    This article reviews what has been published on the rheology of worm-like micellar fluids (WLMFs). It is written primarily for those interested in continuum (non-Newtonian fluid) mechanics: it covers the bulk rheological behaviour of typical WLMFs and rheological equations of state (REoS) that reflect this bulk behaviour; it also covers molecular dynamics and Brownian dynamics models that aim to predict observed behaviour. It is concluded that experimental measurements have been restricted to a limited range of flow kinematics only, and so agreement with particular (suitably parametrised) theoretical models for REoS has not been conclusively validated. It also raises the question of whether WLMFs can be treated as "simple fluids" once shear banding and rheological chaos ensue, as have been observed.

  • Rheology Reviews 2006
    pp. 255-291
    RHEOMETRY FOR BLOOD COAGULATION STUDIES
    P. A. Evans, K. Hawkins & P.R. Williams

    PDF (click to download) Abstract (click to view)

    This review considers some of the various rheometrical approaches that have been adopted to study blood coagulation, with special reference to the rheological assessment of clotting time and studies of the evolution of viscoelasticity during the course of fibrin polymerization and cross-linking. A common feature of many of these studies is that they attempt to detect a liquid-to-solid transition during coagulation and the significance of the Gel Point in blood coagulation studies is discussed. Coagulation studies based on various forms of shear viscosity measurements and complex shear modulus measurements are considered, the latter being based principally on instruments such as the various controlled stress and controlled strain rheometers. Also considered is the long established technique of thromboelastography, while several emerging techniques are described. The latter include damped oscillation rheometry, various forms of wave propagation measurements and other, less widely used techniques such as free oscillation rheometry, quartz crystal microbalance measurements and surface plasmon resonance.

RHEOLOGY REVIEWS 2007

ISBN: Book: 0-9547414-6-3; CD: 0-9547414-7-1

  • Rheology Reviews 2007
    pp. 1-52
    POLYMER MELT VISCOELASTICITY: WHAT WE CAN LEARN FROM MOLECULAR SIMULATIONS
    Vlasis G. Mavrantzas

    PDF (click to download) Abstract (click to view)

    In this review, we discuss how computer simulations at molecular level can help understand the complicated mechanics and flow behaviour of polymeric liquids. We focus, in particular, on one of the most distinctive properties of these materials, their viscoleasticity, quantifying the irreversible conversion of the work done for their deformation to heat loss but also their capability to store part of this work as elastic energy. We restrict our analysis to flexible polymers in the melt state and we describe how one can take advantage of recent advances in the field of atomistic Monte Carlo and Molecular Dynamics simulations in order to explain their relaxation mechanisms and flow properties. This information can be used to validate and parameterize molecular models, and to design better constitutive equations capable of providing a reliable expression for the stress tensor in terms of the imposed flow kinematics and certain, well-defined molecular parameters. The availability of such constitutive equations is important in the development of large-scale numerical approaches with predictive power, since they can help reduce the huge number of experiments typically required in industrial applications for optimising materials or for designing new processes and processing technologies.

  • Rheology Reviews 2007
    pp. 53-134
    QUANTITATIVE TUBE MODEL PREDICTIONS FOR THE LINEAR VISCOELASTICITY OF LINEAR POLYMERS
    Evelyne van Ruymbeke, Chen-Yang Liu & Christian Bailly

    PDF (click to download) Abstract (click to view)

    Tube models derived from the basic ideas of De Gennes and Doi & Edwards on reptation of entangled chains have made tremendous progress in the past 30 years and have now reached a quantitative level for the prediction of linear viscoelasticity of linear polymers. After a concise reminder of key experimental features of dynamic moduli, we first review the fundamental ingredients of quantitative tube models: reptation, contour length fluctuations and constraint release, as well as some important modifications that are proving essential in difficult cases, such as the "Struglinski-Graessley criterion" or the "constraint release Rouse" regime. The main models published since the origin of the theory are next briefly described and compared. They can be classified in two major categories, those derived from the Doi-Edwards theory built on the original reptation concept and those derived from the Milner-McLeish theory, which considers linear chains as two-arms stars able to reptate. We further review published comparisons between experimental data and model predictions for various systems, comprising monodisperse, polydisperse and bidisperse polymers. The latter are the most difficult to predict because they emphasize complex interactions between the relaxation mechanisms. Hence they highlight the current limitations of the models, in particular the influence of constraint release mechanisms on reptation and fluctuations.

  • Rheology Reviews 2007
    pp. 135-178
    FLOWS OF VISCOPLASTIC MATERIALS: MODELS AND COMPUTATIONS
    Evan Mitsoulis

    PDF (click to download) Abstract (click to view)

    Viscoplasticity is characterized by a yield stress, below which the materials will not deform, and above which they will deform and flow according to different constitutive relations. Viscoplastic models include the Bingham plastic, the Herschel-Bulkley model, and the Casson model. All of these ideal models are discontinuous. Analytical solutions exist for such models in simple flows. For general flow fields, it is necessary to develop numerical techniques to track down yielded/unyielded regions. This can be avoided by introducing into the models a continuation parameter, which facilitates the solution process and produces virtually the same results as the ideal models by the right choice of its value. This work reviews several benchmark problems of viscoplastic flows, such as entry and exit flows from dies, flows around a sphere and a cylinder, and squeeze flows. Examples are also given for typical processing flows of viscoplastic materials, where the extent and shape of the yielded/unyielded regions are clearly shown.

  • Rheology Reviews 2007
    pp. 179-260
    MODEL SOFT COLLOIDS OUT OF EQUILIBRIUM: GLASS-LIKE AND RE-ENTRANT TRANSITIONS
    Dimitris Vlassopoulos, Emmanuel Stiakakis & Michael Kapnistos

    PDF (click to download) Abstract (click to view)

    Star polymers with tunable number and size of arms, and thus interactions, represent ideal model systems for exploring the regime of soft material behaviour that interpolates between hard spheres and polymeric coils. This regime is characterized by a rich variety of properties that reflect the combination of polymeric and colloidal features. In this review we discuss some of these properties, and in particular the host of kinetic frustration phenomena encountered with such ultrasoft particles. They include soft colloidal glass-like transitions (a kind of jamming), induced upon increasing volume fraction (by heating or increasing the mass concentration), and the glass melting upon application of thermal (depletion) forces.

RHEOLOGY REVIEWS 2008

ISBN: Book: 978-0-9547414-8-8; CD: 978-0-9547414-9-6

  • Rheology Reviews 2008
    pp. 1-46
    STRONG FLOWS OF VISCOELASTIC WORMLIKE MICELLE SOLUTIONS
    Jonathan P. Rothstein

    PDF (click to download) Abstract (click to view)

    The unique rheological properties of viscoelastic wormlike micelle solutions have led to their broad use as rheological modifiers in consumer products such as paints, detergents, pharmaceuticals, lubricants and emulsifiers. In addition, micelle solutions have also become increasingly important in a wide range of industrial and commercial applications including agrochemical spraying, inkjet printing, turbulent drag reduction and enhanced oil recovery. Until recently, our knowledge of the rheology and flow behavior of these fluids was limited to linear viscoelasticity measurements where wormlike micelle solutions have been shown to behave as ideal Maxwell fluids, and steady shear rheology measurements where wormlike micelles often demonstrate shear banding. In this review, we survey recent experimental and theoretical developments for nonlinear rheology of viscoelastic wormlike micelle solutions and the response of these complex fluids to strong flows. Specific emphasis will be placed on extensional rheology measurements and complex flows having strong extensional components. In many of these flows, viscoelastic wormlike micelle solutions behave in a manner very similar to polymer solutions. Wormlike micelle solutions demonstrate strain hardening of their extensional viscosity which can result in an increased resistance to complex flows such as the flow past a sphere or the flow through porous media. Additionally, the large extensional viscosity of these fluids has led to significant drag reduction in turbulent flows. However, wormlike micelles are self-assembled and as such are quite different than polymer solutions. Under large elastic stresses, wormlike micelles can break apart. This failure and the resulting morphological changes have been linked to a number of newly discovered elastic instabilities not present in polymer solutions. As this review will show, strong flows of wormlike micelle solutions hold a wealth of interesting flow phenomena much of which is yet to be explored.

  • Rheology Reviews 2008
    pp. 47-70
    RHEOLOGICAL ISSUES IN THE PAPER INDUSTRY
    Douglas W. Bousfield

    PDF (click to download) Abstract (click to view)

    The paper industry has a number of processes where the rheology is complex and critical to control for trouble free operation. The rheological properties of pulp suspensions and paper coatings are reviewed here. The flow, rheology and other various phenomena are discussed for pulp suspensions. The particle level models that have been developed for pulp suspensions are compared to experimental results. Paper coating suspension rheology and the coating flow fields are described. Particle level models are discussed and compared to various rheological properties and process issues. Some open questions are identified.

  • Rheology Reviews 2008
    pp. 71-135
    FLOW AND TEXTURE MODELING OF LIQUID CRYSTALLINE MATERIALS
    Alejandro D. Rey

    PDF (click to download) Abstract (click to view)

    A review of flow and texture modeling of liquid crystalline materials with emphasis on carbonaceous mesophases is presented. Two models of nematodynamics are presented and discussed in terms of their ability to resolve time and length scales likely to arise in typical rheological and processing flows. Defect physics and rheophysics are integrated with nematodynamics and specific mechanisms of defect nucleation and annihilation are used to derive texture scale power laws. The integrated nematodynamics models specialized to carbonaceous mesophases are used to analyze: (i) linear and nonlinear viscoelasticity, (ii) rheological flows, and (iii) carbon fiber and flow-induced textures. The linear and nonlinear viscoelasticity reveals the essential nature of these materials : coupling between flow-induced orientation and orientation-induced flow, elastic storage through orientation gradients, and anisotropy. The rheological flow simulations, shown to be in excellent agreement with experimental data, reveal several liquid crystal specific rheological characteristics including shear thinning due to anisotropic viscosities and flow-induced orientation, and negative first normal stress difference due to orientation nonlinearities in the shear stress. Nematodynamic predictions are shown to follows a Carreau-Yasuda liquid crystal equation. Nematodynamics predictions rationalize shear-induced texture refinement in terms of defect nucleation and coarsening mechanisms and are used to derive texture scaling relations in terms of macroscopic, molecular, and flow time scales. This knowledge is then condensed into a generic texture-flow diagram that specifies the required temperature and Deborah number required to produce well oriented monodomain materials. The fine details of mesophase structuring by flow through screens are shown to be captured by nematostatic simulations. Finally the mechanisms behind the carbon fiber textures produced by melt spinning of carbonaceous mesophases are elucidated. The proven range and predictive accuracy of nematodynamics to simulate flows of textured mesophases and the ever-growing industrial interest in lower cost high performance super-fibers and functional materials will fuel the evolution of liquid crystal rheology and processing science for years to come.


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Anton Paar

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